(1) Field of the Invention
The present invention relates generally to a system and method to align a drum and capstan, and more particularly to a system and method to align the stowage drum and capstan of the Deployable Array Working Group (DAWG) installed within a submarine.
(2) Description of the Prior Art
In order to attain the highest level of sonar capabilities, current submarines are outfitted with DAWG systems, allowing the deployment of arrays from the submarine. The DAWG includes a drum for stowing the array aboard the submarine and a capstan unit for deploying the array from the drum and retrieving the array onto the drum. Key to successful operation of the DAWG system is proper relative alignment of the stowage drum and capstan. The alignment is verified after submarine construction and installation of the DAWG system. Previous alignment methods utilized a photogrametry process which included placing targets about the ballast tank containing the DAWG system, obtaining accurate photographs of the targets in relation to the DAWG system and using photogrametry methods to determine the DAWG system alignment based on the target and DAWG system relationships revealed in the photos. However, the photogrametry process is time consuming, taking on the order of several weeks, and thus costly to implement. It has also been determined that the method is prone to error and less accurate than the use of standard theodolite surveying methods. However, the use of theodolites is also time consuming and expensive. Further, theodolites can only be used when the compartment housing the DAWG system is completely dry. Since this compartment is normally flooded when the submarine is waterborne and is partially flooded when the submarine is docked at a repair facility, theodolite measurement could only be used immediately after construction of the submarine. Otherwise, the equipment would have to be brought through water into the ballast tank.
Laser alignment systems are well known in the art. U.S. Pat. No. 3,923,402 to Turcotte recites a laser alignment method and apparatus for aligning paper machinery through the use of a laser reference beam. The exact position of the laser reference beam is determined relative to a pair of benchmarks utilizing triangular reflecting prisms at the benchmarks. The paper machinery can then be positioned and aligned by taking appropriate measurements off the laser reference line. U.S. Pat. No. 4,319,406 to Pehrson, Sr. et al. recites the use of a laser beam to align a series of rollers. Targets are placed on each roller and the laser beam is directed along the desired alignment line such that when the rollers are properly aligned, the laser passes through each target. Starting with the roller nearest the laser, the position of the laser on the target is noted and the proper alignment adjustment is made to allow the laser beam to pass through the target. Each roller is then aligned in turn until the laser beam passes through all the targets. As with a theodolite measurement method, the use of lasers is not practical in an environment where the equipment must be transported under water.